The Alpine Coach list is good, but I wish they included some type of score as to what was major and what was not. Also, if you are a DIYer, your priorities will be different than if you will be paying to have most of the work done.
For example, when I purchased my 2002 Suncruiser 35U, my priorities were mainly to make sure the "truck" portion of the motorhome was in good shape since I felt competent to do most of the "house" repairs myself. Big ticket items like the generator, refrigerator, A/C, etc. are a priority. Extensive exterior side-wall de-lamination (bulging fiberglass) can be a cause for rejection. They can be signs of long-term leakage.
A major issue with Winnebagos is the windshield leak issue, which can run into thousands to fix if the frame is rusting out. The most obvious sign of this are water stains at the front of the dash and on the bottom of the inside windshield trim pieces, which should be removed for inspection of the frame. I suggest you read everything you can about this issue on this forum and others. Googling "Winnebago windshield leak" will come up with pages of items. Here's a YouTube video link to get you started:
Given the weather in Quebec, I'd be surprised if there aren't signs of water leaks unless it's been stored inside and/or the owners have been meticulous in their maintenance. Check around the skylight and vents for water stains and at the bottom corners of the slide outs where they penetrate the sidewalls.
My major after-purchase "surprise" was five leaky hydraulic hoses serving the front slide out (which was working perfectly). The PO had carefully hidden any signs of leakage on the ground and I wasn't knowledgeable enough to inspect the hydraulics more closely since the slide out worked fine. Tires are also expensive (close to $2,000 for six) and age is as important as tread depth. Anything over five years old should be professionally inspected.
Based on my experience, and what I've read on various forums, you should factor in about $4,000 in tune-up/lube/oil change, repairs and replacements even if the motorhome seems to be in good condition. In addition to the hydraulic hoses, mine needed new shocks. You'll probably want to replace the converter with a more modern version with a 3-stage charger along with new batteries. This will run you about $250 or so if you DIY (relatively simple job). Unless it's already been replaced, new flooring may be in order. Again, this can be expensive, especially if you pay to have it done.
Good luck.